: Speech production is an integrative process in which intent is transformed in to action though a series of sensorimotor operations. For most individuals, the speech production process operates smoothly. For persons who stutter (PWS), this process intermittently breaks down. Dysfluencies in speech output, characterized by sound/syllable repetition and/or lengthening, or complete blocks of speech output, disrupt the normal spatial and temporal patterning of movement. The reason or reasons why this apparent maladaptive communicative behavior is manifest in the population, and persists into adulthood is currently unknown. A controversy in the literature is whether and how PWS differ from persons who do not stutter. One possibility is that the speech production system of PWS is not different from those of nonstuttering individuals and stuttering is the secondary characteristic of higher level impairment (cognitive, linguistic, psychological). Alternatively, the locus of the problem is in the speech motor control systems of PWS and the higher level processes interact with unstable output system causing a breakdown of fluent speech. We suggest, based on the available literature that both possibilities exists and further, that most previous attempts to resolve this issue have to limited in scope and technique as to render definitive conclusions premature. In the present proposal, we will examine the performance of stuttering individuals along a number of dimensions reflecting a sampling of cognitive, linguistic, and sensorimotor capabilities. The empirical techniques include the kinematic examination of articulator motion, electromyographic analysis of orofacial muscle activity, the examination of responses to mechanical and auditory disruptions during speaking, reaction times associated with increasing linguistic complexity and attentional demands, and functional Magnetic Resonance Imaging during language processing and production. The research focuses on both theoretical and practical issues in order to maximize the impact of the research on understanding the disorder. Many of the other investigations proposed will provide information on many of the important nervous system operations for communication and the manner in which they may be impaired in stuttering individuals. Other investigations will provide useful clinical information by describing the specific changes in speech production variables that accompany a number of clinical techniques known to reduce the frequency of stuttering. We also attempt to identify differences in movement variance functions preceding experimentally-induced stuttering episodes to determine if these episodes can be predicted from an examination of fluent speech. Once identified, such variables could be used to predict the onset of stuttering episodes and ultimately in treating the disorder.